Turn on Hide Price Until Login for individual products. Each product gets a "Login to purchase" entry in its FluentCart menu, and the module's "Apply to" setting chooses between those products and all products. Stores that already used the module keep applying it to all products, so updating exposes no price; new setups are opt-in. Buy Now, Add to Cart, and quantity controls are now left out of the page per product, so a shop grid can mix hidden and visible products.
Fixes: guest modal checkout for a login-only product now shows the login prompt instead of the HTTP 500 it returned since 2.6.4, and orders containing a login-only product are refused when the buyer must log in, closing carts created before the product required login. Invoice and existing-order payment links are unaffected.
Validation: 21 per-product checks and the scope migration on MariaDB, 13 store-wide checks on FluentCart 1.6.6, real HTTP tests of Buy Now, modal checkout, and order placement for guests and logged-in customers in both modes, a failing pre-fix run, existing checkout cache-buster, currency, and invoice contract checks, PHP/JavaScript syntax, generated assets, and package integrity.